Corrosion Resistance Of 316L Stainless Steel Research Articles

Effect of Chloride Impurity on Corrosion Kinetics of Stainless Steels in Molten Solar Salt for CSP Application: Experiments and Modeling

Solar salt (60 wt% NaNO3 + 40 wt% KNO3) is widely used in the storage system of concentrated solar power plant. However, the chloride within the molten solar salt can affect the corrosion kinetics of stainless steels and hence affect the overall structural integrity. In this work, the corrosion behavior of 304 and 316L stainless steel (SS) in molten solar salt mixtures with different chloride impurities were investigated by immersion tests at 565 °C. Results show that as the content of chloride in the solar salt increases (up to 1.4 wt%), both 304 and 316L SS keep parabolic corrosion kinetics, and the rate constants increase. In comparison with 304 SS, the better corrosion resistance of 316L SS is ascribed to the higher thickness ratio of FeCr2O4 spinel to oxide scale. In addition, to quantitatively describe the effect of chloride impurity on corrosion kinetics of stainless steels, a novel theoretical model based on Fick’s first law is proposed and validated by the experiments.

In vitro study: Bond strength, electrochemical and biocompatibility evaluations of TiO2/Al2O3 reinforced hydroxyapatite sol–gel coatings on 316L SS

To improve the biocompatibility and corrosion resistance of 316L SS (Stainless Steel) metal implants, HAp(hydroxyapatite)/TiO2/Al2O3 nanocomposite coating was created using dip sol-gel method sintered at 550 °C. The weight percentage of TiO2+ Al2O3 in these coatings was 20, 30, and 40% wt. In this study, characterization was performed using FTIR (Fourier-Transform Infrared Spectroscopy), XRD, FE-SEM (Field Emission Scanning Electron Microscope), EDS (Energy Dispersive Spectroscopy), DLS (Dynamic Light Scattering), Pull-off, and AFM (Atomic Force Microscopy) analysis. The potentiodynamic polarization and EIS (Electrochemical Impedance Spectroscopy) were performed in the simulated body fluid (SBF) solution. The samples were immersed in SBF solution for 28 days to investigate the ability to form a bone-like layer on the coatings. The amount of calcium and phosphate in the SBF solution and on the coating surface was measured. The MTT assay was performed to examine human MG63 cells viability for various coatings (24 and 72 h). The results showed that the HAp/TiO2/Al2O3 reinforced coatings have the lowest cracks and porosity and have the highest bond strength to the 316L SS substrate (26.5 MPa). Also, the lowest corrosion current density is related to nanocomposite coatings (HAp + 40%wt Al2O3 + TiO2:0.091 μA/cm2), which is pretty low compared to the uncoated substrate (40.35 μA/cm2) or HAp coating (25.26 μA/cm2). The EIS test results showed that in Nyquist curves, the semicircular diameter is more extensive for nanocomposite coatings, which indicates the higher corrosion resistance of these coatings. Cell culture studies showed that the reinforced coatings were non-cytotoxic to human MG63 cell line (HAp + 30%wt Al2O3 + TiO2:99.50% MG63 cell viability), and these coatings have a higher ability to form a bone-like layer than other coatings. However, adding 40% wt TiO2 + Al2O3 negatively affects biocompatibility (HAp + 40%wt Al2O3 + TiO2:87.7% MG63 cell viability). Therefore, HAp + 30%wt(TiO2 + Al2O3) coatings have biocompatibility, adhesion strength, corrosion resistance higher than other coatings, which means that this improved coating has better properties than hydroxyapatite coatings, and this is a new turning point for biocomposite coatings for medical applications.

Antibacterial durability and biocompatibility of antibacterial-passivated 316L stainless steel in simulated physiological environment

Stainless steel (SS) has been widely applied as one of the most efficient implant metal materials, although corrosion and infection in body environment are still challenging. Herein, an antibacterial passivation method was employed to enhance the antibacterial performance and corrosion resistance of the medical 316L SS. The result proved that the antibacterial-passivated 316L SS exhibited stable antibacterial activity and effectively inhibited the formation of bacterial biofilm. Electrochemical measurements combined with X-ray photoelectron spectroscopy technique were used to study the corrosion resistance and semiconductor behavior of passivated 316L SS immersed in simulated physiological environment. The results indicated that the 316L SS after antibacterial passivation treatment for 1 h, soaking in the medium for 10 days, showed satisfactory corrosion resistance attributing to proper Cu deposition in the passive film. The anodic stripping voltammetry measurement further confirmed that the Cu-bearing passive film could continuously release Cu ions into medium. The zebrafish test demonstrated an excellent in vivo biocompatibility for the 316L SS with antibacterial passivation for 0.5 and 1 h, respectively. In addition, changes of surface roughness, contact angle and chemical composition after antibacterial passivation played an important role in explaining the antibacterial mechanism, which could be clearly divided into contact killing and ionic release killing. Hence, the antibacterial passivation treatment was preliminarily proved as a potential way for enhancing the persistent antibacterial activity and corrosion resistance of 316L SS.

Electrochemical Corrosion and In Vitro Bioactivity of SiO2:ZrO2-Coated 316L Stainless Steel in Simulated Body Fluid

The effect of Si:Zr ratio on the in vitro bioactivity and electrochemical corrosion behavior of SiO2:ZrO2-mixed oxide-coated 316L stainless steel (SS) was evaluated in simulated body fluid (SBF) solution for 72, 120, and 168 h. Growth of Hydroxyapatite (HAp) was accelerated when Si content in the coating was increased. The Zr content in the coating improved the corrosion resistance of 316L SS rather than accelerating the HAp growth. When the Si:Zr ratio was 50:50, the coating exhibited significant improvement in corrosion resistance as well as HAp growth. The mechanism of HAp growth was proposed based on the change in surface zeta potential values of the coatings. Potentiodynamic polarization studies revealed about 10 and 5 times reduction in corrosion current density (i corr) values for SiO2:ZrO2 (50:50)-coated 316L SS after 168 h of immersion compared to SiO2, ZrO2, and Si:Zr (70:30) coatings in SBF solutions thus confirming the superior corrosion resistance. The equivalent circuit parameters derived from electrochemical impedance spectroscopy studies further confirmed significant improvement in charge transfer resistance value even after 168 h of exposure.